ASSOCIATED PLANTS AND ANIMALS 503 



in pollination and dissemination of fruits and seeds. In 

 regions where there are strong prevailing winds only such plants 

 as are adapted to regulate transpiration can grow. Most of our 

 early flowering plants, as the Pines, Oaks, Beeches, and Poplars, 

 are pollinated by the wind, and some of our crop plants, as Corn 

 illustrates, depend largely upon the wind for pollination. For 

 the wide dissemination of the fruits and seeds of many of the 

 common weeds and of some cultivated plants, and also for the 

 spreading of some fungous diseases the wind is responsible. 



Associated Plants and Animals. — A plant must compete 

 with surrounding plants and often with animals for existence. 

 It is common observation that most crop plants will not do well 

 under the shade of trees. The trees cut off the light and make 

 the soil too dry for the crop plants. On the other hand, there 

 are plants which require shade and hence grow best in the woods. 

 In some cases plants are benefited while in other cases they are 

 injured through the association of their roots with the roots of 

 other kinds of plants. For example, when Corn and Clover 

 are grown together, experiments indicate that Corn does better 

 than when it is grown alone. One experimenter grew Oats, 

 Barley, Buckwheat, Wheat, and Flax in pots with and without 

 the underground shoots of Canada Thistle and found all except 

 Buckwheat to grow better with the Canada Thistle than alone. 

 He repeated the experiment, using a young Elm tree instead 

 of the Canada Thistle, and found that all grew more poorly Avith 

 the Elm tree than alone. In Jutland it is found that Spruce 

 trees grow well on waste areas if their roots can associate with 

 those of the Mountain Pine. If there are no Mountain Pines 

 present, the Spruces will not grow. If the Pines are present 

 but are cut before the Spruces get well started, the Spruces die 

 or make a poor growth. No doubt much injury to crops caused 

 by weeds is due to the antagonistic effects of their root systems. 

 The association of certain kinds of nitrogen-fixing Bacteria 

 with the roots of legumes and of parasitic plants with their 

 hosts are familiar examples of a very intimate relation of the 

 life processes of one plant with those of another. In competing 

 for light, as previously pointed out, plants must adjust themselves 

 to each other in various ways. Climbing plants, in securing a 

 better position in reference to light for themselves, frequently 

 injure the plant which they climb. For example. Morning 



